client: add timer() option #159

Job	Run time
Check Style	5s
Check MSRV (1.63)	3m 49s
Test with Miri	42s
Test stable on ubuntu-latest	33s
features	33s
Test stable on windows-latest	1m 52s
Test stable on macOS-latest	1m 14s
Test beta on ubuntu-latest	26s
Test beta on windows-latest	1m 6s
Test beta on macOS-latest	1m 10s
Test nightly on ubuntu-latest	26s
Test nightly on windows-latest	47s
Test nightly on macOS-latest	50s
Build docs	28s
CI is green	1s
	14m 2s

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